Optical film and liquid crystal display using the same

ABSTRACT

A film for a liquid crystal display comprising a fatty acid cellulose ester film having an acetyl group and a propionyl group is disclosed. Sum of degree of acetyl substitution (DSac) and degree of propionyl substitution (DSpr) of the fatty acid cellulose ester film of the film is 2.8 or less, and a retardation value (Rt value) in the thickness direction defined by Formula 1 is 60 to 300 nm.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a Divisional of U.S. patent application Ser. No.09/691,310 filed Oct. 18, 2000, now U.S. Pat. No. 6,503,581.

FIELD OF THE INVENTION

The invention relates to such a film employed in a liquid crystaldisplay as a protective film, view angle enlarging film, an opticallyanisotropic film such as a phase difference film, a polarizing plateemploying film, and a liquid crystal display.

A liquid crystal display operates at low voltage as well as low powerconsumption, and further, can be directly connected to an IC circuit.Specifically, it is possible to decrease its thickness. As a result, itis widely employed in word processors, personal computers, and the like,as the display. The basic structure of said liquid crystal display issuch that polarizing plates are provided on the both sides of the liquidcrystal cell.

In such liquid crystal displays, from the viewpoint of contrast and thelike, those employing a twisted nematic liquid crystal (TN), having atwist angle of 90 degrees, have been replaced with those employing supertwisted nematic liquid crystal (STN) having a twist angle of at least160 degrees.

However, liquid crystal displays, employing STN, utilize doublerefraction or birefringence of the liquid crystal. As a result, thefollowing problems which are tinted blue or yellow have occurred.Viewing angle decreases, and it is difficult to produce acceptable colorimages in TN.

In order to overcome these problems, that is, to compensate for adverseeffects due to double refraction, a technique has been proposed in whicha phase difference plate is provided under the aforementioned polarizingplate. By employing this technique, the aforementioned tint problem isovercome. However, the viewing angle problem is largely unsolved.Further, a technique has been proposed in which a double refraction filmis prepared in which the refractive index in the thickness direction ofsaid film is greater than that in the vertical direction against theoptical axis of double refraction, and the resultant film is employed asthe phase difference plate. Still further, a technique has been proposedin which one plate having a positive double refraction value and theother plate having a negative refraction value are employed as the phasedifference plate, or a multilayer exhibiting such properties is employedas the phase difference plate. Still further, as shown in JapanesePatent Publication Open to Public Inspection No. 7-218724, a polarizingplate is proposed in which at least one of its protective films is aplastic film comprised of acetyl cellulose, having the retardation valueof 30 to 70 nm in the in-plane direction when measured employing lighthaving a wavelength of 590 nm.

As methods to overcome these problems, various types of proposals havebeen made. For example, Japanese Patent Publication Open to PublicInspection No. 63-149624 proposes an F-STN system employing a stretchedresin film, and Japanese Patent Publication Open to Public InspectionNos. 3-87720 as well as 4-333019 proposes a method to carry out colorcompensation employing a film in which molecules of a liquidcrystallizing polymer are subjected to twisted orientation for thepurpose of decreasing its weight as well as its wall thickness whilemaintaining the compensation performance of a D-STN system. The phasedeference compensation board of said liquid crystal display is comprisedof a transparent base board, an oriented layer formed on said baseboard, and a liquid crystal polymer layer which is fixed in a twistedorientation state on said oriented layer.

Further, currently, as disclosed in Japanese Patent Publication Open toPublic Inspection No. 7-191217, trials to improve the viewing angle of aliquid crystal cell have been carried out as compensation of the viewingangle of a TFT and TN liquid crystal display in such a manner that adiscotic liquid crystal film is provided on the upper and lower surfacesof a liquid crystal cell. Said compensation board for the TN type liquidcrystal display is comprised of a transparent base board, an alignmentlayer formed on said base board, and a liquid crystal alignment layerformed on said alignment layer in the same manner as the phasedifference compensation board of the liquid crystal display described inthe aforementioned Japanese Patent Publication Open to Public InspectionNos. 3-87720 and 4-333019.

As described above, in recent years, in STN liquid crystal displays, andalso in TFT and TN liquid crystal displays, demanded is an optical filmhaving more advanced compensation performance than before. As the meansto meet said demand, an optical film, on which a liquid crystal compoundis coated, has been investigated.

On the other hand, techniques have been developed in which improvementof a crystal mode makes it possible to improve the viewing angle. Forexample, Japanese Patent Publication Open to Public Inspection No.2-176625 discloses a liquid crystal display employing the liquid crystalcell of a vertical alignment (VA) liquid crystal mode which orients aliquid crystal compound vertically during non-application of voltage andsubstantially orients the same horizontally during application ofvoltage. The vertical alignment (VA) liquid crystal mode ischaracterized in having a wider viewing angle and higher speed responsecompared to the conventional liquid crystal mode. The trial sample ofthe liquid crystal display of the vertical alignment (VA) liquid crystalmode was already exhibited earlier (based on Nikkei Microdevice No.136,page 147, 1996). The liquid crystal display of the vertical alignment(VA) liquid crystal mode exhibits a wider viewing angle thanconventional liquid crystal displays. However, when compared to CRTs,further improvement is required. In order to improve the viewing angle,it is considered to employ an optical compensation sheet in the samemanner as the conventional liquid crystal mode.

Said VA type liquid crystal display comprises the liquid crystal cellwith a vertical alignment orientation mode in which when no voltage isapplied, liquid crystal molecules are oriented vertical to theorientation plate, while when voltage is applied, they are orientedparallel to the orientation plate. As a result, in said liquid crystaldisplay, black is displayed as genuine black, contrast increases, andthe viewing angle is relatively wider, compared to the TN and STN types.However, in accordance with an increase in size of a liquid crystalscreen, an increase in the viewing angle has been increasingly demanded.

In order to increase the viewing angle of said VA system liquid crystal,the present inventors investigated the protective film for a polarizingplate. During the course of the investigation, it was found that in theVA type liquid crystal display, even though a film, which allows tocontrol the retardation value in the in-plane direction as shown inJapanese Patent Publication Open to Public Inspection No. 7-218724, isemployed, the resulting effects were low.

Further, Japanese Patent Publication Open to Public Inspection No.9-90101 proposes that casting can be carried out without using chlorinebased hydrocarbons as the solvent, by increasing the solvent selectionrange through substituting an acetyl group and a propionyl group of thespecified range, and also proposes fatty acid cellulose esters having alow retardation value in both in-plane and thickness directions with thepurpose such that the high contrast of liquid crystal displays such asthe TFT type and FSTN type in which high contrast has been realized, isnot degraded.

Consequently, the investigation regarding a protective film for apolarizing plate was further conducted. As a result, it was discoveredthat when a film was employed in which the retardation value (Rt valuein the aforementioned Formula 1) in the thickness direction which was avalue showing anisotropy in the in-plane direction as well as in thethickness direction without employing the conventional retardation valuein the in-plane direction in the viewing angle of the VA type liquidcrystal display increased. Further, investigation was carried outregarding a method to increase the retardation value in the thicknessdirection. Thus the present invention was realized.

Further, in an optically anisotropic film prepared by providing a liquidcrystal layer onto a support having a greater RT value, the inventors ofthe present invention discovered that advantageous performance wasobtained not only in a VA type liquid crystal cell but also in a TN typeliquid crystal cell. Still further, at that time, without employing alarge amount of costly liquid crystalline compounds as well as withoutincreasing the support thickness, a preferable optically anisotropicfilm was obtained. Accordingly, it is possible to obtain an opticallyanisotropic film as a less expensive, smaller and lighter part.

Further, when cellulose ester film is produced by dissolving celluloseester and casting the resulting solution, any portion which has beensubjected to insufficient esterification tends to remain in the film asinsoluble foreign matter particles. When the resulting film is employedto produce liquid crystal display elements, it has been found that theinsoluble foreign matter particles cause problems such as hindering theformation of a polarizing state and forming abnormal light emission dueto its difference in the refractive index from cellulose ester. Further,under normal light condition, it was difficult to detect saidabnormality due to the presence of insoluble particles. In recent years,the high precision of liquid crystal displays is progressing andproblems due to such foreign matter particles have increasingly beennoted.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a film for a liquidcrystal display which enables enhancement of viewing angle withoutincreasing the thickness, and provide a polarizing plate as well as aliquid crystal display using the same. Another object of the presentinvention is to provide a film for a liquid crystal display whichminimizes problems due to abnormal light emission, while exhibitingexcellent tearing strength as well as excellent water resistance, and apolarizing plate as well as a liquid crystal display using the same.Still another object of the present invention is to provide a film for aliquid crystal display which is less expensive and thinner, whileexhibiting high performance optical anisotropy, and a polarizing plateas well as a liquid crystal display using the same.

The present invention and its embodiments will now be described.

The other embodiment of the invention is described.

1. An optical film comprised of a fatty acid cellulose ester film havingan acetyl group and a propionyl group, and a retardation value (Rtvalue) in the thickness direction defined by Formula 1 of 60 to 300 nm.

Formula 1:

Rt value=[(n _(x) +n _(y))/2−n _(z) ]×d

wherein n_(x) represents the refractive index of the film in thedirection parallel to the film casting direction, n_(y) represents therefractive index of the film in the direction vertical to the castingdirection, n_(z) represents the refractive index of the film in thethickness direction, and d (in nm) represent the thickness of the film.

2. The film described in 1. above, having a retardation value in thethickness direction of 90 to 200 nm.

3. The film described in 1. above, having a retardation value in thethickness direction of 100 to 175 nm.

4. The film described in 3. above, having a retardation value (Ro value)in the in-plane direction defined by Formula 2 of no more than 10 nm.

Formula 2:

Ro value=(n _(x) −n _(y))×d

wherein n_(x) represents the refractive index of the film in thedirection parallel to the film casting direction, n_(y) represents therefractive index of the film in the direction vertical to the castingdirection, and d (in nm) represent the thickness of the film.

5. The film described in any one of 1. through 4. above, having athickness of 40 to 190 nm.

6. The film described in any one of 1. through 4. above, having athickness of 60 to 190 nm.

7. The film described in any one of 1. through 4. above, having athickness of 75 to 190 nm.

8. The film described in 1. or 2. above, which is produced by castingabsolution which is prepared by dissolving in an organic solvent fattyacid cellulose esters having a degree (DSac) of acetyl substitution of1.5 to 2.3 and a degree (DSpr) of propionyl substitution of 0.6 to 1.2.

9. A production method of an optical film in which when the filmdescribed in 8. above is produced by casting said solution on a belt ordrum, the residual solvent amount is between 5 and 100 percent duringpeeling the film from said belt or drum.

10. In a production method of the film described in 1. above, aproduction method of an optical film wherein a solvent in solution,which is employed for casting, comprises a non-chlorine based solvent inan amount of at least 50 percent.

11. In a production method of the film described in 1. above, aproduction method of an optical film wherein the weight ratio of alcoholbased solvent to the total solution, which is employed for casting, isno more than 0.3.

12. The film described in 1. above, which comprises 1 to 20 weight partsof at least one type of plasticizers comprised of phosphoric acidesters, fatty acid esters and phthalic acid esters with respect to 100weight parts of fatty acid cellulose ester.

13. The film described in 1. above, which comprises 0.005 to 0.3 weightpart of fine particles having an average particle diameter of no morethan 0.1 m with respect to 100 weight parts of fatty acid celluloseester.

14. The film described in 1. above, which comprises 0.8 to 2.0 weightparts of a UV absorbers with respect to 100 weight parts of fatty acidcellulose ester.

15. The film described in 1. above, wherein the number foreign matterparticles having a size of 5 to 50 μm, which are observed under apolarized light cross Nicole state, is no more than 200 per 250 mm ²,and the number of foreign matter particles having a size of at least 50μm is substantially 0.

16. The film described in 15. above, wherein the number foreign matterparticles having a size of 5 to 50 μm, which are observed under apolarized light cross Nicole state, is no more than 200 per 250 mm ².

17. The vertical alignment type liquid crystal display which employs anyone of optical films described in 1., 2., 3., 4., 5., 6., 7., 8., 12.,13., 14., 15., and 16. above.

An optically anisotropic film which comprises a fatty acid cellulosefilm support having an acyl group from 2 to 3 carbon atoms in the same,having thereon at least one liquid crystal orientation film as well asone liquid crystal layer, and further has a relationship represented byformula (I) between the refractive index nx in the x direction in theplane of said cellulose ester film support, the refractive index ny inthe y direction, and the refractive index nz in the thickness direction:

Formula (I)

(nx+ny)/2−nz>0

The aforementioned optically anisotropic film wherein the retardationvalue (Rt value) represented by formula (II) is between 50 and 300 nm.

Formula (II)

[(nx+ny)/2−nx]×d

wherein nx and ny each represent refractive indices in the x direction,and in the y direction in the plane of the cellulose ester film support;nz represents the refractive index of the film in the thicknessdirection; and d (in nm) represents the film thickness.

The retardation value (Rt value) represented by said formula (II) ispreferably between 60 and 250 nm.

The thickness of said optically anisotropic film is preferably between40 and 150 μm.

It is preferable that the degree of acetyl substitution (DSac) of afatty acid cellulose ester film is between 1.5 and 2.5, and the degreeof propionyl substitution (DSpr) is between 0.6 and 1.2.

When a fatty acid cellulose ester film support is cast on a belt or adrum, said film support is preferably peeled from said belt or drumwhile exhibiting a residual solvent amount of 5 to 10 percent.

A solution, employed for casting a fatty acid cellulose ester film on abelt or drum, preferably comprises chlorine-free solvents in an amountof at least 50 percent by weight with respect to the entire solventamount.

It is preferable that a solvent in a solution employed for casting afatty acid cellulose ester film on a support comprises at least onealcohol-free solvent and the amount of an alcohol based solvent is 30percent or less with respect to the total solvent amount.

A fatty acid cellulose ester film support preferably comprises at leastone plasticizer selected from phosphoric acid ester derivatives, fattyacid ester derivatives, and phthalic acid ester derivatives in an amountof 1 to 20 percent by weight with respect to the fatty acid celluloseester.

A fatty acid cellulose ester film support preferably comprises fineparticles having an average particle diameter of 0.1 μm or less in anamount of 0.005 to 0.3 percent by weight with respect to the fatty acidcellulose.

It is preferable that at least one liquid crystal layer be provided on atransparent film support and the Rt ratio of the liquid crystal layer tothe transparent support, which is represented by the Formula 3 describedbelow, is 1.2 or less.

Formula 3

Rt ratio=(Rt′/Rt)

wherein Rt′ represents the retardation value in the thickness directionof the liquid crystal layer, and Rt represents the retardation value inthe thickness direction of the transparent support.

Herein, Rt′ is represented by the following formula:

Rt′=[(nx′+ny′)/2−ny′]×d′

wherein nx′ and ny′ each represent refractive indices in the x′direction and the y′ direction, in the plane of the liquid crystallayer, while nz′ represents the refractive index in the thicknessdirection of the liquid crystal layer, and d′ (in nm) represents thethickness of the liquid crystal layer.

Rt is expressed by the following formula:

Rt=[(n _(x) +n _(y))/2−n _(z) ]×d

wherein n_(x) and n_(y) each represent refractive indices in the xdirection and the y direction in the plane of the transparent support,while n_(z) represents the refractive index in the thickness directionof the film, and d (in nm) represents the thickness of the film.

The Rt ratio is preferably 0.8 or less.

The Rt ratio of the liquid crystal layer to the fatty acid celluloseester film support, which is represented by the following Formula 4, ispreferably 1.2 or less.

Formula (4)

Rt ratio=(Rt′/Rt)

wherein Rt′ represents the retardation value in the thickness directionof the liquid crystal layer, and Rt represents the retardation value inthe thickness direction of the fatty acid cellulose ester film support.

Herein, Rt′ is expressed by the following formula:

Rt′=[(nx′+ny′)/2−nz′]×d′

wherein nx′ and ny′ each represent refractive indices in the x′direction and the y′ direction in the plane of the liquid crystal layer,while nz′ represents the refractive index in the thickness direction ofthe liquid crystal layer, and d′ (in nm) represents the thickness of theliquid crystal layer.

Rt is expressed by the following formula:

Rt=[(nx+ny)/2−nz]×d

wherein nx and ny each represent refractive indices in the x directionand the y direction in the plane of the fatty acid cellulose ester filmsupport, while nz represents the refractive index in the thicknessdirection of the film, and d (in nm) represents the thickness of thefilm.

The Rt ratio is preferably 0.8 or less.

One of the uses of said optically anisotropic film is for a viewingangle compensation film for a liquid crystal display.

The liquid crystal mode is preferably either a twist nematic mode or avertical alignment mode.

It is preferable that a liquid crystalline compound, which constitutes aliquid crystal layer, be a monomer having a chemically reactive group,and after being oriented on an alignment layer, said orientation isfixed while being hardened employing either light or heat.

The example of said liquid crystalline compound is a discotic liquidcrystal.

Another example of said liquid crystalline compound is a liquidcrystalline polymer.

An optically anisotropic film wherein luminescent points which areobserved when two polarizing plates are provided on both surfaces of acellulose ester film support so as to shield transmission light, thenumber of said points having a size exceeding 50 μm is zero per 250 mm²,and the number of said points having a size of 5 to 50 μm is 200 or lessper 250 mm².

The number of luminescent points having a size of 5 to 50 μm ispreferably 100 or less per 250 mm².

It is possible to use an optically anisotropic film as a liquid crystaldisplay being provided on both sides of a liquid crystal cell.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view of a liquid crystal display.

DETAILED DESCRIPTION OF THE PREFERABLE EMBODIMENT

The present invention will now be detailed.

The film for a liquid crystal display of the present invention iscomprised of a fatty acid cellulose ester film having an acetyl groupand a propionyl group. Listed as films for a liquid crystal display maybe optical compensation films such as a protective film for a polarizingplate, a phase difference film, an optically anisotropic film, a viewingangle enhancing film, and the like, as well as films which exhibitcombined functions of these films, and the like. The term “fatty acidcellulose ester” means fatty acid ester of cellulose.

Further, the film for a liquid crystal display of the present inventionmay or may not comprise a liquid crystal layer as well as a liquidcrystal alignment layer. The liquid crystal layer is a layer formed byliquid crystal compound. The liquid crystal layer itself may or may notshow liquid crystal characteristics. For example, the liquid crystallayer may be formed by polymerizing liquid crystal compound. Thealignment of liquid crystal is fixed by chemical reaction caused byfunction of heat and/or light energy liquid crystal layer. Singlemolecular liquid crystal compound having.positive refraction index ispreferable since it has low viscosity and is easily subjected toalignment of liquid crystal by heat. In particular, liquid crystalcompound having ethylenical unsaturated bond may be fixed by hardeningthrough photo-radical reaction by employing photopolymerizationinitiator.

The film for a liquid crystal display of the present invention, whichcomprises or does not comprise said liquid crystal layer, may preferablybe applied to the vertical alignment (VA) type liquid crystal display.On the other hand, a film comprising the liquid crystal layer maypreferably be applied to a twist nematic (TN) type liquid crystaldisplay.

The alignment layer is preferably provided between the liquid crystallayer and the support.

Further, the total substitution degree of the fatty acid cellulose esterfilm of a film for a liquid crystal display of the present invention is2.8 or less, preferably 2.1 to 2.8, and more preferably 2.3 to 2.8, inparticular 2.5 to 2.75 is preferable. By adjusting the substitutiondegree to said value, it is possible to obtain a film for a liquidcrystal display having excellent optical anisotropy without increasingthe film thickness. In addition, the total substitution degree asdescribed herein means the sum of the degree of acetyl substitution(DSac) and the degree of propionyl substitution (DSpr). Further, DSac ispreferably between 1.5 and 2.3, and is more preferably between 0.9 andbelow 2.0. Still further, DSpr is preferably between 0.5 and 1.2, morepreferably between 0.6 and 1.2, and in particular preferably between 0.9and 1.2.

The substitution degree as described herein means the percentage of theamount of a so-called combined fatty acid, and preferably an averagenumber of acyl groups bonding to one glucose unit in cellulose. The Dsacis determined based on the measurement as well as the calculation ofacetylation degree in ASTM-D817-91 (Test Method of Cellulose Acetate andthe like. DSpr can be determined based on ASTM-D814-96. Further, theretardation value (RT) in the thickness direction of a fatty acidcellulose ester film is a positive value, and is between 60 and 300 nm.Further, it is possible to obtain Rt employing the formula describedbelow:

Formula 1

Rt=[(nx+ny)/2−nz]×d

wherein nx represents the refractive index of a cellulose ester film inthe maximum refractive index direction in the plane of a fatty acidcellulose ester film; ny represents the refractive index of a fatty acidcellulose ester film in the vertical direction with respect to the nxdirection; nz represents the refractive index of a fatty acid celluloseester film in the thickness direction; and d (in nm) represents thethickness of a fatty acid cellulose ester film.

In addition, nx may be regarded as the refractive index parallel to thecasting direction of a fatty acid cellulose ester film. In the samemanner, ny may be regarded as the refractive index vertical to thecasting direction of said film.

Further, Rt is preferably between 90 and 300 nm, is more preferablybetween 90 and 200 nm, is further more preferably between 90 and 175 nm,and is still further more preferably between 100 and 175 mm. Inaddition, the Rt value of the present invention can be obtained bydetermining refractive indices nx, ny, and nz in such a manner thatmeasurement of three-dimensional refractive index is carried out at awavelength of 590 nm at 23° C. and 50 percent relative humidity,employing an automatic double refractometer (for instance, a KOBRA-21ADHmanufactured by Oji Keisokukiki Co., Ltd.).

Further, the film for a liquid crystal display of the present inventionis.comprised of a fatty acid cellulose ester film having a retardationvalue (Ro), in the plane direction defined by formula 2, of 30 nm orless:

 Ro=(nx−ny)×D  (Formula 2)

Ro is more preferably 20 nm or less, and is further more preferably 10nm or less.

Further, a formula of (nx+ny)/2−nz>0 is preferably held.

Still further, the thickness of the fatty acid cellulose ester film ispreferably between 40 and 190 μm, is more preferably between 60 and 190μm, is further more preferably between 75 and 190 nm, and sill furthermore preferably between 75 and 150 μm.

Tearing strength of the cellulose ester film is preferably over 10 g,more preferably 15 g or more and most preferably 20 g or more. Themeasurement is preferably based on ASTMD-1992.

Further, the number average molecular weight of fatty acid celluloseester is preferably between 70,000 and 300,000, and is preferablybetween 90,000 and 200,000.

Said fatty acid cellulose ester can be synthesized employing acidanhydrides and acid chlorides as the acylation agents. When saidacylation agents are acid anhydrides, organic acids (for instance,acetic acid) as well as methylene chloride are employed as the reactionsolvents, and acid catalysts such as sulfuric acid are employed as thecatalysts. When the acylation agents are acid chlorides, basic compoundsare employed as catalysts. In the most common synthesis method,cellulose is subjected to esterification employing organic acidcomponents comprising organic acids (acetic acid and propionic acid)corresponding to an acetyl group and a propionyl group, or those acidanhydrides (acetic anhydride and propionic anhydride), and thuscellulose esters are synthesized. The employed amount of acetylationagents and propionylation agents is regulated so that synthesized estersare in the aforementioned range. The employed amount of reactionsolvents is preferably between 100 and 1,000 weight parts with respectto 100 weight parts of cellulose. The employed amount of acid catalystsis preferably between 0.1 and 20 weight parts with respect to 100 weightparts of cellulose. Reaction temperature is preferably between 10 and120° C. Further, after completion of the acylation reaction, if desired,the substitution degree may be adjusted employing hydrolysis(saponification). After completion of the reaction, the resultingreaction mixture is separated employing common means such asprecipitation, washed, and is subsequently dried. Thus fatty acid ester(cellulose acetate propionate) is obtained.

For example, synthesis can be carried out employing the method describedbelow. First, added to 299 g of cellulose are 907 g of acetic acid and223 g of propionic acid, and the resulting mixture is mixed at 54° C.for 30 minutes. After cooling the mixture, esterification is carried ourby adding 318 g of acetic anhydride cooled to about 20° C., 813 g ofpropionic anhydride, 10.6 g of sulfuric acid, and 6.3 g of propionicacid. During esterification, the maximum temperature is maintained at40° C. After conducting the esterification for 150 minutes, a mixedsolution consisting of 295 g of acetic acid and 98.5 g of water as thereaction termination agent is added over 20 minutes, and excessiveanhydrides are subjected to hydrolysis. The reaction composition ismaintained at 60° C., and 886 g of acetic acid and 295 g of water areadded. After one hour, an aqueous solution containing 18.0 g ofmagnesium acetate is added, and then sulfuric acid in the reactionsystem is neutralized. The degree of acetyl substitution and propionylsubstitution of the obtained cellulose acetate propionate are 2.1 and0.8, respectively, and the number average molecular weight is about120,000.

Employed individually or in combination as the fatty acid celluloseester of the present invention are fatty acid ester synthesizedemploying cotton linters and fatty acid ester synthesized from woodpulp. Cellulose ester synthesized employing cotton linters is preferablyemployed at a larger ratio, because it is more readily peeled from abelt or drum, and thus enhances productivity. When the content ofcellulose ester synthesized employing cotton linters is at least 60percent, the peeling properties are markedly improved. Therefore, thecontent is preferably at least 60 percent, is more preferably at least85 percent, and is most preferably 100 percent.

Listed as solvents which dissolve the fatty acid cellulose ester of thepresent invention and form a dope may be methylene chloride, methylacetate, ethyl acetate, amyl acetate, acetone, tetrahydrofuran,1,3-dioxolan, 1,4-dioxolan, cyclohexanone, 2,2,2-trifluoroethanol,2,2,3,3-tetrafluoro-1-propanol, 1,3-difluoro-2-propanol, and the like.Incidentally, chlorine based solvents such as methylene chloride may beemployed without causing any problem from the technical aspect. It ispreferred that amount of the chlorine based solvent is not more than 50%in the solvent. Methyl acetate, ethyl acetate, acetone, and the like,cause the least environmental problem. Specifically, the content ofmethyl acetate is preferably at least 50 percent by weight with respectto the total organic solvents. Acetone is preferably employed in anamount of 5 to 30 percent by weight with respect to the total organicsolvents, together with methyl acetate, because it makes it possible todecrease the dope viscosity. In the present invention, containing of aslittle as possible chlorine based solvents means that the content of thechlorine based solvents is no more than 10 percent with respect to thetotal organic solvents, is more preferably no more then 5 percent, andis most preferably 0 percent.

In addition to the organic solvents described above, alcohols havingfrom 1 to 30 carbon atoms are preferably incorporated into the fattyacid cellulose ester dope of the present invention in an amount of 1 to30 percent. When alcohols are incorporated, after casting the dope ontoa support, solvents start to evaporate and the web (a dope layer formedby casting a dope on a casting support is designated as the web) isgelled and the web is strengthened. Thus it is possible to more readilypeel the web from the support. Further, it is possible to obtain effectswhich accelerate the dissolution of fatty acid cellulose ester. Listedas alcohols having from 1 to 4 carbon atoms are methanol, ethanol,n-propanol, iso-propanol, n-butanol, sec-butanol, and tert-butanol. Ofthese, ethanol is preferred, based on the stability of the resultingdope, its boiling point, drying properties, non-toxicity, and the like.

The solid portion concentration in a dope is commonly, and preferably,between 10 and 40 percent. From the viewpoint of obtaining excellentflatness of a film, the viscosity of a dope is preferably controlled tobe in the range of 100 to 500 poise. The dope, which has been preparedas described above, is filtered employing a filter media, defoamed, andsubsequently conveyed to the next process, employing a pump.

Plasticizers, matting agents, UV absorbers, antioxidants, dyes, and thelike may also be incorporated into said dope.

Fatty acid ester cellulose, having an acetyl group as well as apropionyl group employed in the present invention, exhibits effects of aplasticizer. As a result, sufficient film properties are obtainedwithout the addition of plasticizer, or at most addition in smallamounts. However, plasticizers may be added for other purposes. Forexample, for the purpose to enhance the moisture resistance of film,added may be alkyl phthalyl alkyl glycolates, phosphoric acid esters,carboxylic acid esters, phthalic acid ester, fatty acid ester, citricacid ester and the like.

Listed as alkyl phthalyl alkyl glycolates are, for example, methylphthalyl methyl glycolate, ethyl phthalyl ethyl glycolate, propylphthalyl propyl glycolate, butyl phthalyl butyl glycolate, octylphthalyl octyl glycolate, methyl phthalyl ethyl glycolate, ethylphthalyl methyl glycolate, methyl phthalyl propyl glycolate, methylphthalyl butyl glycolate, ethyl phthalyl butyl glycolate, butyl phthalylmethyl glycolate, butyl phthalyl ethyl glycolate, propyl phthalyl butylglycolate, butyl phthalyl propyl glycolate, methyl phthalyl octylglycolate, ethyl phthalyl octyl glycolate, octyl phthalyl methylglycolate, octyl phthalyl ethyl glycolate, and the like.

Listed as phosphoric acid esters may be, for example, triphenylphosphate, tricresyl phosphate, cresyl diphenyl phosphate, phenyldiphenyl phosphate, octyl diphenyl phosphate, trioctyl phosphate,tributyl phosphate, and the like.

Carboxylic acid esters include, for example, phthalic acid esters andcitric acid esters. Listed as said phthalic acid esters may be dimethylphthalate, diethyl phthalate, dimethoxyethyl phthalate, dimethylphthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethyl hexylphthalate, and the like, while listed as said citric acid esters may be,for example, acetyl trimethyl citrate, acetyl triethyl citrate, andacetyl tributyl acetate.

In addition, butyl oleate, methyl acetyl recinoleate, dibutyl sebacate,triacetin, and the like are preferably employed individually or incombination.

If desired, two or more types of plasticizers may be employed incombination. Phosphoric acid ester based plasticizers are preferredbecause when employed at a ratio of no more than 50 percent, thecellulose ester film is barely subjected to hydrolysis and exhibitsexcellent durability. Further, a low content of phosphoric acid basedplasticizers is preferred. Particularly preferred is the sole use ofphthalic acid ester based or glycolic acid ester based plasticizers. Ofthese, methyl phthalyl methyl glycolate, ethyl phthalyl ethyl glycolate,propyl phthalyl propyl glycolate, butyl phthalyl butyl glycolate, andoctyl phthalyl octyl glycolate are preferred, and particularly employedis ethyl phthalyl ethyl glycolate. Alternatively, two or more types ofthese alkyl phthalyl alkyl glycolates are employed in combination. Theamount of plasticizers employed for said purpose is preferably between 1and 30 percent with respect to the cellulose ester, and is mostpreferably between 4 and 13 percent. These compounds may be added alongwith cellulose ester and solvents during preparation of a celluloseester solution or may be added during the preparation of the solution orafter said preparation.

With the purpose to improve yellow hue of film, dyes are incorporated.Since cellulose ester film is tinted slightly yellow, dyes are preferredwhich are capable of tinting to gray as seen in common photographicsupports. Thus blue and violet dyes are preferably employed. However,being different from the photographic supports, since it is unnecessaryto minimize light piping, only a small amount of dye addition may besufficient. Specifically the content of dyes is preferably between 1 and100 ppm with respect to the cellulose ester, and is more preferablybetween 2 and 50 ppm. Gray may be obtained by appropriately combining aplurality of dyes.

When films are not sufficiently slippery, they are subjected to blockingwith each other, and occasionally, ease of handling is degraded. Mattingagents such as fine inorganic particles including silicon dioxide,titanium dioxide, sintered calcium silicate, hydrated calcium silicate,aluminum silicate, magnesium silicate, crosslinked polymers, and thelike are preferably incorporated into the film, based on the presentinvention.

Further, in order to decrease the haze of a film, fine particles such assilicon dioxide are preferably subjected to surface treatment employingorganic substances. Cited as preferred organic substances for saidsurface treatment are halosilanes, alkoxysilanes, silazanes, siloxanes,and the like. The matting effect increases as the average particlediameter of fine particles increases, while transparency increases assaid diameter decreases. Accordingly, the average primary particlesdiameter of fine particles is no more than 0.1 μm, preferably between 5and 50 nm, and more preferably between 7 and 14 nm. Listed as fineparticles of silicon dioxide are Aerosil 200, 200V, 300, R972, R972V,R974, R202, R812, OX50, TT600 and the like, all of which aremanufactured by Nihon Aerosil Co., ltd. Of these, preferably listed areAerosil R972, R972V, R974, R202, R812, and the like. Said matting agentsare preferably blended to obtain a film haze of no more than 0.6percent, and a friction coefficient of no more than 0.5. The amount ofmatting agents, which are employed for said purpose, is preferablybetween 0.005 and 0.3 percent with respect to fatty acid celluloseester. These fine particles usually exist in an aggregated form in thefilm and it is preferable to make the surface of the film roughness of0.01 to 1.0 μm.

Liquid crystal displays are increasingly employed in the openatmosphere. Thus it is important to provide a protective film for apolarizing plate with the function to absorb ultraviolet rays. UVabsorbers are preferably incorporated into the film of the presentinvention. Preferred as UV absorbers are those which efficiently absorbultraviolet rays having a wavelength of no longer than 370 nm from theviewpoint of minimizing the degradation of liquid crystals and whichminimally absorb visible light having a wavelength of at least 400 nmfrom the viewpoint of producing an excellent liquid crystal display.Specifically, the transmittance at a wavelength of 370 nm is required tobe no more than 10 percent. The added amount of UV absorbers ispreferably in the range of 0.5 to 5 percent with respect to the fattyacid cellulose ester, and is more preferably in the range of 0.6 to 2.0percent. The amount is particularly preferably 0.8 to 2.0 wt %.

UV absorbers, which are employed to achieve said purposes, preferablyhave no absorption in the visible light range. Listed as such UVabsorbers are benzotriazole based compounds, benzophenone basedcompounds, salicylic acid based compounds and the like. Examples of suchUV absorbers include 2-(2′-hydroxy-5-methylphenyl)benzotriazole,2-(2′-hydroxy-3′,5′-di-t-butylphenyl)benzotriazole,2-(2′-hydroxy-3′-di-t-butyl-methylphenyl)benzotriazole,2,4-dihydroxybenzophenone, 2-hydroxy-4-methoxybenzophenone,2-hydroxy-4-n-octocybenzophenone, 4-dodecyloxy-2-hydrooxybenzophenone,2,2′,4,4′-tetrahydroxybenzophenone,2,2′-dihydroxoy-4,4′-dimethoxybenzophenone, phenyl salicylate, methylsalicylate, and the like.

In the present invention, at least one of these UV absorbers ispreferably employed, and at least two of different UV absorbers may beincorporated.

The addition methods of said UV absorbers are as follows. They may bedissolved in organic solvents such as alcohol, methylene chloride,dioxolan, and the like and the resulting solution is added to a dope.Alternatively, they may be added directly to a dope. UV absorbers suchas inorganic powders, which are not soluble in organic solvents, may bedispersed into a mixture of organic solvents and cellulose ester,employing a dissolver or a sand mill, and added to a dope.

In the present invention, the employed amount of UV absorbers iscommonly between 0.1 and 2.5 percent with respect to the celluloseester, is preferably between 0.5 and 2.0 percent, and is more preferablybetween 0.8 and 2.0 percent. However, it is not preferred that theemployed amount of UV absorbers exceeds 2.5 percent, becausetransparency tends to be degraded.

In order to enhance the heat resistance of a film, hindered phenol basedcompounds are preferably employed. The added amount of these compoundsis preferably between 1 ppm and 1.0 percent by weight with respect tothe cellulose ester, and is more preferably between 10 and 1,000 ppm.Further, in addition to these compounds, heat stabilizers such as alkaliearth metal salts comprised of calcium, magnesium, and the like, mayalso be added.

In addition to the aforementioned compounds, further, added may beantistatic agents, flame retarders, lubricants, oils, and the like.

When a film is prepared employing cellulose ester which comprisesinsoluble foreign matter particles, they cause diffused reflection. Thuswhen such film is employed in a liquid crystal display, light from thecrystal cell is scattered to cause degraded visibility of the display.It is difficult to detect insoluble foreign matter particles underordinary light. However, when observation is made in such a manner thattwo polarizing plates are arranged in the right angle (cross Nicole)state and a cellulose ester film is placed between them then it isilluminated from one side, it is possible to detect gleaming foreignmatter particles in a dark visual field. Thus it is possible to readilydetermine the sizes as well as the numbers of foreign matter particles.The number of foreign matter particles having a size of 5 to 50 μm ispreferably no more than 200 per 250 mm² and the number of foreign matterparticles having a size of at least 50 nm is preferably substantially 0.More preferably, the number of foreign matter particles having a size of5 to 50 μm is no more than 100 per 250 mm². Foreign matter particleshaving a size of less than 5 μm are visually not problematic, howevernumber of the foreign matter particles is preferable as less as possibleif the size is less than 5 μm. On the other hand, foreign matterparticles having a size of at least 50 μm are barely formed during theproduction of cellulose ester employing common methods. Foreign matterparticles such as metal, sealing materials, and the like having a sizeof at least 50 μm, are removed during production process of celluloseester. Due to that, foreign matter particles in a dope, prepared bydissolving cellulose ester, are filtered to remove foreign matterparticles. Usable filters are those which exhibit resistance to organicsolvents. Employed as such filters may be, for example, sintered metalfilters, metallic fiber filters, resinous filters (woven fabric andnonwoven fabric), ceramic filters, glass filters, and paper filters.Further, it is possible to suitably choose the sieve opening of filtersdepending upon the size of foreign substance to be removed, andselection is generally made from the range of 0.1 to 100 μm. Filters maybe employed individually or may be employed in a plurality of them inseries. Specifically, filtration is preferably carried out employing apaper filter having a water filtration time of at least 20 seconds and afiltration pressure of no more than 1.6 Mpa, is more preferably carriedout employing a paper filter having a water filtration time of at least30 second and a filtration pressure of no more than 1.0 Mpa, and isfurther more preferably carried out employing a paper filter having awater filtration in time of at least 40 seconds and a filtrationpressure of no more than 1.0 Mpa. It is preferable to use paper filtersat least two of them overlapping. It is possible to control thefiltration pressure by suitably controlling the filtration flow rate andthe filtration area.

The dissolution Process is one in which cellulose ester flakes aredissolved, while stirring, in organic solvents mainly comprised of goodsolvents for said flakes, employing a dissolution vessel, and thereby acellulose ester solution (hereinafter referred to as a dope) isprepared. In order to carry out said dissolution, there are variousmethods such as a method in which dissolution is carried out at a normalatmospheric pressure, a method in which dissolution is carried out at atemperature lower than the boiling point of the primary solvent, amethod in which dissolution is carried out at a temperature higher thanthe boiling point of the main solvent under an increase of pressure, acooling dissolution method in which dissolution is carried out at alowering temperature, as described in J. M. G. Cowie et al., Makromolhem., volume 143, page 105 (1971), and Japanese Patent Publication Opento Public Inspection Nos. 9-95544 and 9-95557, and others, a method inwhich dissolution is carried out at a high pressure, and the like. Theresultant dope is filtered employing filter materials, is then defoamed,and is subsequently pumped to the next process.

An obtained dope is cast onto a support. Employed as casting methods maybe a band method or a drum method. Subsequently, a film, which isprepared as described above, is peeled from the support. Thereafter,tension is applied to the resulting film which is dried while beingconveyed through a drying zone.

Casting process: a process in which a dope is conveyed to a pressure diethrough a pressure type metering gear pump, and at the casting site,said dope is cast from said pressure die onto a support for casting(hereinafter occasionally referred to as a support) which is aninfinitely moving endless metal belt or a rotating metal drum. Thesurface of the support for casting is specular. Listed as other castingmethods are a doctor blade method in which the thickness of the dopelayer is regulated employing a blade, and also a reverse roll coatermethod in which regulation is carried out employing a roll which rotatesin the reverse direction. However, said pressure die is preferred inwhich the slit shape at the mouth piece portion can be regulated and thefilm thickness is readily regulated to be uniform. The pressure dieincludes a coat hanger die, a “T” die, and the like, and any of thesemay preferably be employed. In order to increase the casting speed, atleast two pressure dies may be provided and at least two layers may besimultaneously cast while dividing the dope.

Solvent evaporation process: a process in which a web is heated on thesupport for casting and solvents are thereby evaporated. In order toevaporate solvents, methods include one in which air is blown from theweb side, and/or a method in which heating is carried out from thereverse surface of the support employing liquid, and another in whichheating is carried out from the surface as well as the revere surfaceemploying heat radiation. Of these, the reverse surface liquid heatingmethod is preferred due to high drying efficiency. Further, thesemethods are preferably combined.

Peeling process: a process in which a web, which has been subjected toevaporation of solvents on the support, is peeled at the peeling site.The peeled web is conveyed to the subsequent process. When the residualsolvent amount (refer to the formula described below) is too excessive,it may be difficult to peel the web. On the contrary, when peeling iscarried out after fully drying the web on the support, a part of the webmay peel prior to the peeling site. Listed as a method to increase thecasting speed is a gel casting method (in which peeling can be carriedout even though the amount of residual solvents is relatively great).Said gel casting methods include a method in which poor solvents withrespect to the cellulose ester are added to a dope and gelling iscarried out after casting said dope, and also a method in which gellingis carried out by decreasing the temperature of the support, and thelike. Further, also included is a method in which metal salts are addedto the dope. By strengthening the web through gelling the dope on thesupport, it is possible to carry out earlier peeling and to increase thecasting speed. When peeling is carried out at the time when the residualsolvent amount is still relatively great, the web may be too soft. Thusduring peeling, the flatness of the web tends to be degraded, andwrinkles and longitudinal streaks tend to be formed. Accordingly, theresidual solvent amount is determined so that productivity and qualityare balanced.

Drying process: a process which dries a web employing a drying apparatusin which said web is alternatively passed through staggered rolls and/ora tenter apparatus in which said web is conveyed while the web width ismaintained by holding both web edges employing pins or clips. A commondrying method is one in which both surfaces of the web are subjected tohot air flow. Instead of air, employed is a method in which heating iscarried out employing microwaves. Too rapid drying tends to degrade theflatness of the finished film. High temperature drying is preferablycarried out when the residual solvent amount is no more than 8 percent.During the entire drying process, drying temperatures are commonlybetween 40 and 250° C., and are preferably between 70 and 180° C. Dryingtemperature, drying air volume, and drying time vary depending onemployed solvents. Thus drying conditions may be suitably selecteddepending on types of employed solvents and their combination.

In the drying process, the web tends to shrink in the width directiondue to the evaporation of solvents. When rapid drying is carried out ata relatively high temperature, shrinkage increases further. Drying ispreferably carried out while minimizing the resulting shrinkage so thatthe finished film exhibits excellent flatness. From this viewpoint, adrying method (a tenter method), as shown, for example, in JapanesePatent Publication Open to Public Inspection No. 62-45525, is preferredin which the entire or a part of the drying process is carried out whileholding both edges of the web in the width direction employing clips.

Winding process: a process in which after decreasing the residualsolvent amount to no more than 2 percent, the resulting web is wound. Bydecreasing the residual solvent amount to no more than 0.4 percent, itis possible to obtain a film having excellent dimensional stability.Employed as winding methods may be those which are commonly employed.Said methods include a constant torque method, a constant tensionmethod, a taper tension method, an inner stress constant program tensioncontrol method, and the like. Any of these may be selected and employed.

The residual solvent amount is expressed employing the formula describedbelow:

Residual solvent amount (in percent)=(M−N)/N×100; wherein M representsthe weight of a web at an optional time, and N represents the weightwhen M is dried at 110° C. for 3 hours.

The thickness of a fatty acid cellulose ester film is preferablyregulated while controlling the dope concentration, the pumping volume,the slit distance of the mouth piece of the die, the excluding pressureat the die, and the speed of the support for casting. Further, a methodwhich makes the film thickness uniform is preferred in which said filmthickness is controlled using feedback information from a film thicknessdetecting means.

In the process from casting to drying, air may be employed as an ambientgas in the drying apparatus. On the other hand, drying may also becarried out in an ambience comprised of inert gases such as nitrogengas, carbon dioxide gas, and the like. However, it must be noted thatthe concentration of evaporated solvents in the drying environment doesnot approach their explosion limits.

In order to obtain a film having a retardation value in the thicknessdirection (Rt value) of the present invention, listed are the methodsdescribed below. However, the present invention is not limited to thesemethods.

(1) In the process until a film is peeled from a belt or drum, as theresidual solvent amount during peeling decreases, the Rt valueincreases, while as said residual solvent amount increases, the Rt valuedecreases. In this case, the residual solvent amount during peeling ispreferably between 5 and 100 percent, is more preferably between 5 and80 percent, and further more preferably between 10 and 45 percent.

(2) As peeling tension as well as conveyance tension in a drying zoneincreases, the Rt value decreases, while when they decrease, the Rtvalue increases: Peeling tension is preferably between 50 and 400 N/m,is more preferably between 100 and 300 N/m, and is further morepreferably between 100 and 250 N/m. Further, conveyance tension in thedrying zone is preferably between 50 and 200 N/m, is more preferablybetween 80 and 150 N/m, and is further more preferably between 80 and120 N/m.

(3) There is a pin tenter method in which a film is dried while beingstretched or a drying method employing a clip tenter method. In thiscase, as the stretching factor increases, the Rt value increases, whileas said factor decreases, the Rt value decreases. The stretching factoris preferably between 2 and 50 percent, is more preferably between 5 and40 percent, and is further more preferably between 10 and 30 percent.

Further, the thickness of the protective film for a polarizing plate ofthe present invention is preferably between 75 and 190 μm, is morepreferably between 100 and 175 μm, and is further more preferablybetween 120 and 160 μm.

In the present invention, in order to minimize the variation of theretardation value (Rt) due to humidity, as well as to obtain excellentviewing angle characteristics, the equilibrium moisture content ratio ofthe optical film of the present invention as well as the protective filmfor a polarizing plate (said optical film which is-prepared by adheringa polarizing plate) of the present invention, is preferably no more than6 percent. Said moisture content ratio is more preferred as thepercentage decreases to no more than 5 percent, to no more than 4percent, to no more than 3 percent, to no more than 2 percent, andfinally to no more than 1 percent. The particularly preferred moisturecontent is substantially zero. “Substantially zero”, as described in thepresent invention, means no more than 0.5 percent.

Incidentally, said equilibrium moisture content ratio is obtained asfollows. Karl Fischer's moisture meter, specifically a micro-volumemoisture meter CA-06 and a moisture evaporation device VA-06(manufactured by Mitsubishi Kasei Co., Ltd.) are employed. After heatingat 120° C. for 45 minutes, it is possible to calculate the moisturecontent ratio employing the formula described below:

Moisture content ratio (in percent)=remaining moisture weight/filmweight after heating treatment×100.

Employed as the polarizing layer provided on the surface of saidprotective film for a polarizing plate may be those which areconventionally known in the art. For example, employed are those whichare obtained by treating a film comprised of hydrophilic polymer such aspolyvinyl alcohol with dichroic dyes such as iodine and then stretched,or which are prepared by treating a plastic film such as polyvinylchloride to result in polyene orientation. The polarizing plate is thenstructured in such a manner that said protective film for a polarizingplate is laminated onto at least one surface of said polarizing layer.The polarizing plate is prepared by applying composition described inU.S. Pat. No. 6,049,428 on the polarizing plate protective film.

The polarizing plate prepared as described above is provided on onesurface or both surfaces of a VA type liquid crystal cell. By employingthe resulting polarizing plate, the liquid crystal display of thepresent invention is obtained.

When optical anisotropy is achieved by applying a liquid crystallinecompound onto a transparent support, it is possible to carry out desiredorientation by applying said liquid crystalline compound onto thealignment layer which has been prepared on said transparent support.

Listed as methods to orient a liquid crystalline compound, without usingthe alignment layer, may be a method in which a liquid crystallinecompound is heated to a temperature at which liquid crystal propertiesare exhibited, and is then subjected to application of an electric fieldor a magnetic field. It is possible to obtain an orientation stateemploying a method in which heated air is blown or a liquid crystallinecompound flows in the range of liquid crystal temperature by decliningthe base board. Of these, from the viewpoint of ease of its production,it is preferable that after providing an alignment layer, a rubbingtreatment is carried out and applying a liquid crystalline compound ontothe resultant alignment layer then carries out orientation.

Now, said alignment layer will be described. Specifically listed are thefollowing resins as well as base boards, though the present invention isnot limited to these. For example, listed are polyimides,polyamidoimides, polyamides, polyether imides, polyether ether ketones,polyether ketones, polyketone sulfides, polyether sulfones,polysulfones, polyphenylene sulfides, polyphenylene oxides, polyethyleneterephthalate, polybutylene terephthalate, polyethylene naphthalate,polyacetals, polycarbonates, polyallylates, acrylic resins, polyvinylalcohols, polypropylene, cellulose based plastics, epoxy resins, phenolresins, and the like.

The alignment layer can be obtained in such a manner that after applyingany of the aforementioned orientation materials onto a transparentsupport, and subsequently drying the resultant coating, a rubbingtreatment is carried out.

A polyimide layer (preferably polyimide having fluorine atoms), which iswidely employed as an LCD alignment layer, is preferred as the alignmentlayer. It is possible to obtain said layer by applying, onto atransparent support, polyamic acid (for example, LQ/LX Seriesmanufactured by Hitachi Kasei Co., Ltd., and SE Series manufactured byNissan Kagaku Co., Ltd) and applying thermal treatment to the resultantcoating and then rubbing the resultant coated layer.

The aforementioned rubbing treatment may be carried out utilizing atreatment method which is widely employed as an LCD liquid crystalorientation process. Namely, it is possible to employ a method in whichorientation is obtained by rubbing the surface of the alignment layer inthe definite direction employing paper, gauze, felt, rubber, nylon,polyester fiber, and the like. Commonly, the surface of the alignmentlayer is rubbed several times employing a cloth prepared by uniformlyplanted fiber having a uniform length and diameter.

When liquid crystalline compounds employed in the present invention areliquid crystallizing polymers, listed as chemical structure are mainchain type liquid crystalline polymers such as, for example, polyesters,polyimides, polyamides, polyesters, polycarbonates, polyester imides,and the like. Further, listed as side chain type liquid crystallinepolymers are, for example, polyacrylates, polymethacrylates,polysiloxanes, polymalonates, and the like.

As methods for coating liquid crystalline compounds, a solution preparedby dissolving said liquid crystalline compounds in bulk, or an organicsolvent can be coated employing methods such as curtain coating,extrusion coating, roll coating, dip coating, spin coating, printcoating, spray coating, and slide coating, and the like.

When a solution is coated, after said coating, the solvent is removed,and it is possible to obtain a liquid crystal layer having a uniformthickness.

It is possible to fix the orientation of the liquid crystal in theliquid crystal layer through chemical reaction utilizing the action ofheat and/or light energy. Specifically, monomeric liquid crystallinecompounds generally exhibit low viscosity and the orientation of theresultant liquid crystal tends to vary due to thermal causes.Accordingly, it is possible that the liquid crystalline compounds havingan ethylenic unsaturated linkage group are subjected to fixation throughhardening reaction such as light radical reaction and the like,employing a photopolymerization initiator.

In the present invention, when the photopolymerization initiator isemployed during fixing the orientation, in order to generate radicals,it is possible to employ light sources described below. For example, arepreferred light sources such as a high pressure mercury lamp, a metalhalide lamp, and the like, which can effectively emits near ultravioletrays. Those having a maximum molar absorption coefficient of at least100 are preferred, and those having the same of at least 500 are morepreferred. If desired, employed as radiations for photopolymerizationmay be electron beam, ultraviolet rays, visible light, and infrared rays(heat rays). Generally, however, preferred are ultraviolet rays. Listedas ultraviolet ray emitting sources may be low pressure mercury lamps(such as a bactericidal lamp, a fluorescent light chemical lamp, and ablack light), high pressure discharge lamps (such as a high pressuremercury lamp, and a metal halide lamp), and short arc discharge lamps(such as an ultra-high pressure mercury lamp, a xenon lamp, and amercury xenon lamp).

On the other hand, when polymerization initiators are employed, thefollowing compounds may be listed: for example, azobis compounds,peroxides, hydroperoxides, redox catalysts, and the like, such aspotassium persulfate, ammonium persulfate, tert-butyl peroctoate,benzoyl-peroxide, isopropyl percarbonate, 2,4-dichlorobenzoyl peroxide,methyl ethyl ketone peroxide, cumene hydroperoxide, dicumyl peroxide,azobisisobutyronitrile, 2,2′-azobis(2-aminodipropane)hydrochloride, orbenzophenones, acetophenones, benzoins, thioxanthones, and the like.These are detailed in “Shigaisen Koka System (Ultraviolet Ray Hardeningsystem)”, Sogo Gijutsu Center, pages 63 to 146, 1989.

Further, for the polymerization of compounds having a epoxy group,generally employed as ultraviolet ray activating cationic catalysts areallyldiazonium salts (such as hexafluorophosphate, andtetrafluoroborate), diallyliodonium salts, VIa Group allylonium salts(such as allylsulfonium salts having an anion such as PFe, AsFe, andSbFe).

When liquid crystalline monomers are selected, an important factor isthe availability of liquid crystalline compounds substituted with afunctional group which is capable of subjecting said liquid crystallinecompounds to result in hardening reaction. By selecting such compounds,one of useful methods is available in which after orienting liquidcrystalline compounds, the resultant orientation is fixed employing theaforementioned hardening reaction due to light or heat.

On the other hand, when liquid crystalline compounds are liquidcrystalline polymers, it is unnecessary to fix the orientation of liquidcrystals employing hardening reaction, that is the aforementionedchemical reaction. In the temperature range in which an opticallyanisotropic film is employed without causing problems, for example, whena liquid crystalline polymer has a liquid crystal transition temperatureof 90° C. or higher, after applying said liquid crystalline polymer ontoan alignment layer, the resultant coating is heated at a temperaturewithin the range of the liquid crystal transition temperature to resultsin orientation and then cooled to room temperature. By so doing, theorientation of the liquid crystal is maintained.

Further, it is possible to assume such a case that a support issubjected to deformation at a temperature at which the orientation ofthe liquid crystalline polymer is carried out. In such a case, aftersubjecting a heat resistant film to the aforementioned orientationtreatment, a liquid crystal layer may be transferred to the transparentsupport of the present invention via an adhesive layer.

In order to minimize optical deformation such as abrasion and the likewhich are formed during maintaining the orientation and preparing apolarizing plate, a protective layer may be provided. Listed asmaterials for said protective layer may be polymers such as polymethylmethacrylate, acrylic acid/methacrylic acid copolymers,styrene/anhydrous maleiimide copolymers, polyvinyl alcohol,poly(N-methylolacrylamide), styrene/vinyl toluene copolymers,nitrocellulose, polyvinyl chloride, chlorinated polyolefin, polyester,polyimide, vinyl acetate/vinyl chloride copolymers, ethylene/vinylacetate copolymers, polyethylene, polypropylene, polycarbonate, and thelike, and derivatives thereof. It is possible to provide said protectivelayer in such a manner that a solution comprised of any of these.polymers is prepared, is applied to a support while employing theaforementioned coating method, and is subsequently dried.

When liquid crystalline compounds of the present invention are thosehaving discotic structure units, compounds may be employed which aredescribed in, for example, Japanese Registered Patent Nos. 2587398,2640083, 2641086, 2692033, 2692035, 2767382, 2747789, 2866372, andothers.

When liquid crystalline compounds of the present invention are those ofpolymers, employed may be compounds having structures which aredescribed in, for example, Japanese Registered Patent Nos. 2592694,2687035, 2711585, 2660601, and others, and Japanese Patent PublicationOpen to Public Inspection Nos. 10-186356, 10-206637, 10-333134, andothers.

Commonly listed as liquid crystalline compounds except for discoticliquid crystals as well as liquid crystalline polymers are rod-shapedmonomeric liquid crystals. From the viewpoint of the fixation oforientation, preferred are liquid crystalline compounds having anunsaturated ethylenic group. For example, employed may be compoundshaving structures described in, for instance, Japanese PatentPublication Open to Public Inspection Nos. 9-281480, and 9-281481.

Regarding a compensation film to control optical characteristics, thegreater retardation value of said film in the thickness direction is notalways preferred, and there is the preferable range. In order to obtaina preferable retardation value as a whole, when the ratio of theaforementioned retardation value (Rt′ value) of a liquid crystal layerto the retardation value (Rt value) of a transparent support satisfiesthe following relationship, the transparent support having the liquidcrystal layer exhibits suitable characteristics as the compensation filmto control optical characteristics in liquid crystal displays:

Formula 3

Rt ratio=(Rt′/Rt)≦1.2

wherein Rt′ is the retardation value in the thickness direction of theliquid crystal layer, and Rt is the retardation value in the thicknessdirection of the transparent support.

Herein, Rt′ has the following relationship.

Rt′=[(nx′+ny′)/2−nz′]×d′

wherein nx′ and ny′ each represent main refractive indices in the x′direction and the y′ direction in the plane of the liquid crystal layer,and nx′ and ny′ may be the same or different; while nz′ represents therefractive index in the thickness direction of the liquid crystal layer;and d (in nm) represents the thickness of the liquid crystal layer.

Further, Rt is expressed by the following formula.

Rt=[(nx+ny)/2−nz]×d

wherein nx and ny each represent main refractive indices in the xdirection and the y direction in the plane.of the transparent support;while nz represents the refractive index in the thickness direction ofsaid film; and d (in nm) represents the thickness of said film. in theabove formulas, the x and x′ directions in the plane as describedwherein mean the directions parallel to the film casting direction,while the y and y′ directions mean the directions vertical to thecasting direction.

In a more preferred embodiment, Rt ratio=(Rt′/Rt)≦0.8 is satisfied.

The retardation value of a liquid crystal layer is obtained as follows.Specifically, the retardation value of an optical film, prepared byapplying a liquid crystal layer to a transparent support, is determined,and the retardation value of the liquid crystal layer is obtained basedon the difference from the retardation value of the support film.

When liquid crystalline compounds constituting a liquid crystal layerare monomers having a chemically reactive group, after being oriented onan alignment layer, the resultant orientation is preferably fixed whilebeing hardened employing light or heat.

Further, the polarizing plate of the present invention is one which issandwiched between a first film and a second film. Incidentally, anotherfilm as well as a layer may be positioned between said first film andsaid polarizer, and between said second film and said polarizer. Atleast one of said first film and said second film is the film for aliquid crystal display of the present invention. Further, the film for aliquid display of the present invention may be directly adhered ontosaid polarizer. Alternatively, one surface or both surfaces of saidpolarizer may be adhered to the polarizing plate protective filmcomprised of TAC and the like, and onto said polarizing plate protectivefilm, the film for liquid crystal display of the present invention maybe adhered.

Further, the liquid crystal display of the present invention comprises afirst polarizing plate, a liquid crystal cell, and a second polarizingplate which is provided on the inner side of the first polarizing plateas well as the liquid crystal cell. The inner side is the opposite sideagainst outer side such as fresh air side or observer side. Stillfurther, the first polarizing plate comprises a first polarizer, a firstprotective film for the polarizing plate provided on the surface of thefirst polarizer on the side which does not face the liquid crystal cell,and a second protective film for the polarizing plate provided on thesurface of the first polarizer on the side which faces the liquidcrystal cell. The second polarizing plate comprises a second polarizer,a third protective film for the polarizing plate provided on the surfaceof the second polarizer on the side which faces the liquid crystal cell,and a fourth protective film for the polarizing plate provided on thesurface of the second polarizer on the side which does not face theliquid crystal cell.

At least one of the first film, the second film, the third film, and thefourth film is the film for a liquid crystal display of the presentinvention. Further, another film as well as another layer may beprovided between any one of the first to the fourth films and thepolarizer. Further, the film for a liquid crystal display of the presentinvention may be directly adhered onto the polarizer so as to enhancethe function as a protective film for a polarizing plate. The protectivefilm for a polarizing plate, which is prepared employing TAC, may beadhered onto one surface or both surfaces of the polarizer, and the filmfor a liquid crystal display of the present invention may be adheredonto said protective film for a polarizing plate.

Further, in this liquid crystal display, at least one of the second filmand the third film is preferably the film for a liquid crystal displayof the present invention. Both the second film and the third film aremore preferably the film for a liquid crystal display of the presentinvention.

Listed as liquid crystal displays can be vertical alignment (VA) typeliquid crystal displays and twist nematic type (TN) type liquid crystaldisplays such as STN, TN, and the like. Of course, TFT type liquidcrystal displays may also be used.

FIG. 1 is a schematic view of one example of a liquid crystal display.Numeral 5 is a light source and numeral 4 is a liquid crystal cell.Numeral 31 is a first polarizing plate and numeral 32 is a secondpolarizing plate. First polarizing plate 31 comprises first film 21,second film 22, and first polarizer 110. Second polarizing plate 32comprises third film 23, fourth film 24, and second polarizer 120. Inthis example, second film 22 as well as third film 23 is the film for aliquid crystal display of the present invention, and first film 21 aswell as fourth film 24 is a protective film for a polarizing plate,which is prepared employing triacetyl cellulose (TAC). Needless to say,the liquid crystal display of the present invention is not limited tosaid embodiments.

EXAMPLES

In the following, the present invention will be specifically describedwith reference to examples. However, the present invention is notlimited to these examples.

Example 1

(Preparation and Evaluation of Fatty Acid Cellulose Ester Film)

The compositions described below were placed in a tightly sealedpressure vessel, heated to 80° C., and completely dissolved whilestirring under a pressure of 500 kPa, while maintaining saidtemperature.

Cellulose acetate propionate (CAP) 120 weight parts (substitution degreeis described in Table 1) 2-(2′-hydroxy-3′,5′-di-t-butylphenyl) 1 weightpart (UV absorber) Ethyl phthalyl ethyl glycolate 4 weight parts(plasticizer) Fine silica particles (AEROSIL 200 manufactured 0.1 weightpart by Nihon Aerosil Co., Ltd.) (0.016 μm) Methyl acetate 300 weightparts Ethanol 45 weight parts

The resulting dope was cooled to 40° C., while the pressure was reducedto normal pressure. The dope set aside overnight, and was then subjectedto a deforming process. Thereafter, the resulting solution was filtered,employing Azumi filter paper No. 244, manufactured by Azumi Roshi Co.,Ltd. The resulting dope was cooled and maintained at 35° C., and wasuniformly cast on a 6 m long endless rotating stainless steel belt(having an effective length of 5.5 m) which was mounted on two drums.The cast dope was dried for two minutes on the same stainless steel beltof which opposite surface was continually brought into contact with 15°C. water. The solvents were evaporated until the residual solvent amountreached 20 percent. Then peeling from the stainless steel belt wascarried out under a peeling tension of 150 N/m. Subsequently, whileholding both edges of the peeled film, drying was carried out at 130° C.Further, while conveyance was carried out under a conveyance tension of130 N/m, employing numerous rolls, drying was further carried out. ThusFilm No. 1, having a thickness of 120 μm, was obtained. Films No. 2through No. 11 were prepared in the same manner as Film No. 1 exceptthat cellulose elements, the added amounts and the types of solvents,plasticizers, residual solvent amount, and film thickness were varied asshown in Table 1. CAP represents cellulose acetate propionate of thepresent invention. The degree of acetyl substitution and propionylsubstitution was between 1.5 and 2.1 and between 0.6 and 1.2,respectively. TAC represents cellulose triacetate with a degree ofacetyl substitution of 2.8.

The resulting films were subjected to measurement and evaluation,employing the methods described below. Tables 1 and 2 show the results.

(Substitution Degree of Fatty Acid Cellulose Ester)

The substitution degree was measured-employing a saponification method.Dried cellulose ester was accurately weighed and dissolved in a mixedsolvent consisting of acetone and dimethylsulfoxide (at a volume ratioof 4:1). Thereafter, a specified aqueous 1 mol/liter sodium hydroxidesolution was added and saponification was carried out at 25° C. for twohours. Excess sodium hydroxide was titrated with 0.5 mol/liter sulfuricacid, employing phenolphthalein as the indicator. Further, blank testswere carried out employing the same method as above. Still further, thesupernatant of the solution completing the titration was diluted, andthe composition of organic acids was measured based on a common methodemploying an ion chromatograph. The substitution degree (in percent) wascalculated employing the following:

TA=(Q−P)×F/(1,000×W)

DSac=(162.14×TA)/(1−42.14×TA+(1−56.06×TA)×(AL/AC)

DSpr=DSac×(AL/AC)

wherein P is the volume (in ml) of 0.5 mol/liter sulfuric acid necessaryfor titrating a sample; Q (in ml) is the volume of 0.5 mol/litersulfuric acid necessary for the blank test; F is the titer of 0.5mol/liter sulfuric acid; W (in g) is the sample weight; TA (in mol/g) isthe total organic acid amount; AL/AC is the mole ratio of acetic acid(AC) measured employing the ion chromatograph to other organic acids(AL); DSac is the degree of acetyl substitution; and DSpr is the degreeof propionyl substitution.

(Number Average Molecular Weight of Fatty Acid Cellulose Ester)

Measurements were carried out under the conditions described below,employing a high speed liquid chromatography.

Solvent: methylene chloride

Column: MPW×1 (manufactured by Toso Co., Ltd.)

Sample concentration: 0.2 W/V percent

Flow rate: 1.0 ml/minute

Injected sample volume: 300 ml

Standard sample: polystyrene

Temperature: 23° C.

(Residual Solvent Amount)

Residual solvent amount (in percent)=(M−N)N×100; wherein M is the weightof the film (the web) after winding, and N is the weight when M is driedat 110° C. for 3 hours. (Retardation Value (Rt Value) in the ThicknessDirection)

Employing an automatic double refractometer, KOBRA-21ADH, (manufacturedby Oji Keisoku Kiki Co., Ltd.), 3-dimensional refractive indices weremeasured at a wavelength of 590 nm at 23° C. and at 55 percent relativehumidity, and refractive indices n_(x), n_(y), and n_(z) were obtained.The retardation value (Rt value) in the thickness direction wascalculated employing Formula 1 described below.

Formula 1:

Rt value=[(n _(x) +n _(y))/2−n _(z) ]×d

wherein n_(x) represents the refractive index of a film in the directionparallel to the film casting direction, n_(y) represents the refractiveindex of a film in the direction perpendicular to the casting direction,n_(z) represents the refractive index of the film in the thicknessdirection, and d (in nm) represent the thickness of a film. (RetardationValue (Ro value) in the in-plane direction)

Employing an automatic double refractometer, KOBRA-21ADH, (manufacturedby Oji Keisoku Kiki Co., Ltd.), three-dimensional refractive indices aremeasured at a wavelength of 590 nm at 23° C. and at 55 percent relativehumidity, and refractive indices n_(x) and n_(y), are obtained. Theretardation value (Ro) in the in-plane direction is calculated employingFormula 2 described below:

Formula 2:

Ro value=(n _(x−n) _(y))×d;

wherein n_(x) represents the refractive index of a film in the directionparallel to the film casting direction, n_(y) represents the refractiveindex of a film in the direction perpendicular to the casting direction,and d (in nm) represent the thickness of the film.

TABLE 1 Number Substitution Average Solvent Type and Film Com- DegreeMolecular Added Amount No. ponent DSac/DSpr Weight (in weight parts) 1CAP 2.0/0.8 approximately MA300 ET45 100,000 2 CAP 1.9/0.7 approximatelyMA350 ET35  90,000 3 CAP 1.7/1.0 approximately MA300 ET45 100,000 4 CAP1.8/0.9 approximately MA300 AC50 120,000 5 TAC 2.8/0.0 approximatelyMC450 ET50 100,000 6 CAP 2.0/0.8 approximately MA300 ET45 100,000 7 CAP2.0/0.8 approximately MA300 ET45 100,000 CAP: cellulose acetatepropionate TAC: cellulose triacetate MA: methyl acetate ET: methanol MC:methylene chloride AC: acetone

TABLE 2 Plasticizer Residual Layer Film (in weight Solvent Thickness No.parts) (in %) (in μm) Rt Ro Remarks 1 EPEG 5 20 120 130 3 invention 2TPP 7 15 120 160 4 invention EPEG 3 3 EPEG 5 42 120 120 2 invention 4TPP 8 65 120 110 4 invention EPEG 2 5 TPP 15 80 120  55 10  invention 6EPEG 5 40  80  95 5 com- parative 7 EPEG 5 28 140 140 6 invention EPEG:ethyl phthalyl ethyl glycolate TPP: triphenyl phosphate

Example 2

(Preparation and Evaluation of Liquid Crystal Display)

Film No. 1 of Example 1 was treated with an aqueous 2.5 mol/liter sodiumhydroxide solution at 40° C. for 60 seconds and subsequently washed withwater for 3 minutes. Thus an alkali-treated film, in which a saponifiedlayer was formed, was obtained.

Subsequently, a 120 μm thick polyvinyl alcohol film was immersed in 100weight parts of an aqueous solution containing one weight part of iodineand 4 weight parts of boric acid, and then stretched to 4 times originallength at 50° C. by a factor of 4 at 50° C. Thus a polarizing film wasprepared. A polarizing plate was prepared by adhering saidalkali-treated film onto both surfaces of the resulting polarizing film,employing a 5 percent aqueous totally saponified type polyvinyl alcoholsolution as the adhesive. No. 1 Liquid Crystal Display was obtained byproviding the resulting polarizing plate on both surfaces of a VA typeliquid crystal cell.

Liquid Crystal Displays No. 2 through 11 were prepared in the samemanner as above, employing Films No. 2 through 11 of Example 1.

These films were subjected to measurement and evaluation employing themethods described below. Table 3 shows the results.

(Viewing Angle Characteristics)

Each of the obtained liquid crystal displays was subjected to whitedisplay, black display, and 8-gradation gray display, employing a VG365Nvideo pattern generator manufactured by AMT Co., Ltd. Then a contrastratio during white/black display was measured in each angle of upper,lower, right, and left. An angle, which shows contrast ratio ≧10, wasdenoted as the viewing angle.

TABLE 3 Liquid Viewing Angle Properties Crystal (in degrees) GeneralDisplay No. Upper Lower Left Right Evaluation 1 72 55 65 60 A 2 74 59 6565 A 3 72 57 63 62 A 4 70 55 60 60 A 5 45 40 45 40 D 6 60 50 62 62 B 772 57 63 63 A

As can be seen from Table 3, it was found that in the liquid crystaldisplay, which employs cellulose ester film comprising a propionylgroup, the Rt value was at least 60 nm and the viewing angle of saidliquid crystal display increased. The films according to the inventionare found to have wide viewing angle.

Example 3

(Evaluation of Fatty Acid Cellulose Ester Film)

Films No. 1, 5, and 6 were subjected to measurement and evaluationemploying the methods described below. Table 4 shows the results.

(Transmittance)

Transmittance of light having a wavelength of 550 nm was measuredemploying a spectrophotometer (U-3400 manufatured by HitachiSeisakusho).

(Moisture and Heat Resistance)

Two film sheets were prepared by blanking a film. A polyurethaneadhesive was applied to one surface of the resulting film sheet. Then apolarizing film was prepared by adhering the resulting sheet onto bothsurfaces of a polarizing element (30 nm) comprised of polyvinyl alcoholand dichroic dyes. The thus obtained polarizing film was cut into100×100 mm squares, and was adhered onto a glass plate, employing aacryl based adhesive, and stored at 80° C. and 90 percent relativehumidity for 1,000 hours. Thereafter, the peeling state of said film wasobserved and the degree of coloration or chromaticity (“b” value) in thechromaticity diagram was determined.

(Tear Strength of Film)

The tear strength was measured in accordance with ASTM-D1, 992.

A 50×63.5 mm film sheet was subjected to 12.7 mm long cut along thecenter of the sheet in the width direction, and the tearing strength wasmeasured at 23° C. and 55 percent relative humidity, employing a digitaltearing tester manufactured by Toyo Seiki Seisakusho Co., Ltd.

(Dynamic Friction Coefficient)

The dynamic friction coefficient was measured in accordance withJIS-K-7125 (1987).

A 120×300 mm long film sheet was fixed on a supporting stand and an80×200 mm film sheet was placed on it so that the surface and theopposite surface came into contact. Further, a 200 g dead weight wasplaced on them, which were horizontally pulled at a rate of 100mm/minute. Force F necessary for the start of movement was determined.

Dynamic friction coefficient=F (in N)/weight of the dead weight (in N)

(Number of Foreign Matter Particles)

A sample was placed between two polarizing plates which were arranged ina polarized light cross Nicol state. Light was then applied to onesurface of said polarizing plate. Employing a microscope, the number offoreign matter particles per 25 mm² at 10 arbitrary areas was measuredwhich were observed as white spots due to the transmission of light onthe other surface of said polarizing plate. Said measurement wasrepeated 5 times, and the averaged value was designated as the number offoreign matter particles. Employed as microscopic conditions weretransmission light and a magnification factor of 30.

TABLE 4 Moisture and Heat Resistance Coloration Tearing Dynamic Numberof Trans- Degree Strength Friction Foreign Film mittance (in “b” (in g/Coeffi- Matter Classi- No. (in %) value) sheet) cient Particles fication1 92 0.23 46 0.9  66 present inven- tion 4 91 0.25 50 0.8 120 presentinven- tion 5 91 0.38 30 3.0 450 com- parative cracking

From Table 4, it was found that Samples No. 1 and No. 2 exhibitedexcellent properties for commercial use.

Example 4

In the example, the following methods of measurement as well asevaluation were employed.

<Substitution Degree of Fatty Acid Cellulose Esters>

The substitution degree was determined employing a saponificationmethod. Dried cellulose ester was accurately weighed, and afterdissolving said ester in a solvent mixture consisting of acetone anddimethyl sulfoxide (in a volume ratio of 4:1), 1N aqueous sodiumhydroxide solution was added in an predetermined amount. Subsequentlythe resultant mixture underwent saponification at 25° C. for 2 hours. Aphenolphthalein solution was added as the indicator and excess sodiumhydroxide was titrated employing 1N sulfuric acid in addition, a blanktest was carried out employing the same method as described above.Further, the supernatant of the solution, which had been subjected totitration, was diluted, and the composition of organic acids wasdetermined according to the conventional method, employing ionchromatographs. Then substitution degree (in percent) was calculated bythe following formula.

TA=(Q−P)×F/(1,000×W)

DSac=(162.24×TA)/{1−42.14×TA+(1−56.06×TA)×(AL/AC)}

DSpr=DSac×(AL/AC)

wherein P represents the volume (in ml) of 1N sulfuric acid necessaryfor titrating a sample; Q represents the volume (in ml) of 1N sulfuricacid necessary for said blank test; F represents the titer of 1Nsulfuric acid; W represents the weight of a sample; TA represent thetotal amount (in mol/g) of organic acids; AL/AC represents the moleratio of acetic acid (AC) to the other organic acids (in this case,propionic acid) (AL), determined by the ion chromatograph); DSacrepresents the degree of acetyl substitution; and DSpr represents thedegree of propionyl substitution.

<Number Average Molecular Weight of Cellulose Esters>

Measurement was carried out under the following conditions, employing ahigh-speed liquid chromatography.

Solvent: methylene chloride

Column: MPW×1 (manufactured by Toso Co., Ltd.)

Sample concentration: 0.2 weight/volume percent

Flow rate: 1.0 ml/minute

Injection volume of sample: 300 μl

Standard sample: polystyrene

Temperature: 23° C.

<Preparation of Cellulose Ester Film>

A composition was prepared as described below.

Composition (1)

Cellulose acetate propionate (CAP) 120 weight parts (the substitutiondegree as well as number average molecular weight is described in Table4) 2-(2′-Hydroxy-3′,5′-di-tert-butylphenyl) 1 weight part benzotriazole(UV absorber) Ethyl phthalyl ethyl glycolate 5 weight parts Fine silicaparticles (Aerosil 200 having 1 weight part 0.016 μm, manufactured byNihon Aerosil Co.) Methyl acetate 300 weight parts Ethanol 45 weightparts

Compositions (2) through (9) were prepared in the same manner asComposition (1), except that each of cellulose acetate propionate, ethylphthalyl ethyl glycolate, and solvents of ethyl acetate as well asethanol was varied as shown in Table 4.

Each of the aforementioned compositions was placed in a tightly sealedpressurized vessel; was heated to 80° C. under 5 atmospheric pressure;and was dissolved while stirring under said temperature. The dope wascooled to 40° C., and the pressure was decreased to normal atmosphericpressure. The resultant dope was put aside overnight. After defoamingoperation, the resultant dope was filtered employing Azumi filter paperNo. 244 under a filtration pressure of 16 kg/cm² (1.57 Mpa).

Subsequently, the resultant dope was cooled and maintained at 35° C.,and was then uniformly cast onto a 6-meter long endless stainless steelbelt (having an effective length of 5.5 m) which was mounted on twodrums and was rotated. The cast dope was dried for two minutes on saidstainless steel belt of which temperature was controlled in such amanner that the reverse side of said belt was brought into contact withwater at 35° C., and subsequently was cooled on said belt on which thereverse side was brought into contact with water at 15° C. Thereafter,the solvent was evaporated until the peeling residual solvent amountreached the value in Table 2, and a resultant film was peeled from saidstainless steel belt under a peeling tension of 150 Newton/m. Then thepeeled film was dried at 130° C. while maintaining the film dimension atboth edges. Thus, were obtained 80 μm thick Cellulose Ester Film Samples101 through 109 and Cellulose Ester Film Samples 110 through 114 inwhich thickness and the like was varied.

The thickness of each film was measured employing a micrometer.

The retardation value (Rt value) of each film was shown in Table 2. Saidretardation value (Rt value) was determined as described below.

<Retardation Value (Rt Value)>.

Employing an automatic double refractometer, KOBRA-21ADH (manufacturedby Oji Keisokukiki Co., Ltd.), three-dimensional refractive indices weredetermined at a wavelength of 590 nm under an ambience of 23° C. and 55%RH, and thus refractive indices, nx, ny and nz, were obtained. Theretardation value (Rt value) was calculated in accordance with theformula II described below.

Formula (II)

Rt value=[(nx+ny)/2−nz]×d

wherein nx represents the refractive index of the film in the directionparallel to the film casting direction, and ny represents the refractiveindex of the film in the direction vertical to the film castingdirection, while nz represents the refractive index in the thicknessdirection of said film; and d (in nm) represents the thickness of saidfilm.

<Coating of Liquid Crystal Layer>

A gelatin layer (having a thickness of 0.1 μm) was applied onto each oftransparent supports shown in Table 2, and then straight chain alkylmodified polyvinyl alcohol (MP203, manufactured by Kuraray Co., Ltd.)was further applied onto the resultant layer. After drying at 80° C.employing hot air, a rubbing treatment was carried out and an alignmentlayer was formed.

Employing a wire bar, onto the resultant alignment layer, applied was acoating composition prepared by dissolving 1.6 g of liquid crystallizingdiscotic compound LC-1, 0.4 g of phenoxydiethylene glycol acrylate(M101, manufactured by Toa Gosei Co., Ltd.), 0.05 g of cellulose acetatebutyrate (CAB531-1, manufactured by Eastman Chemical Co.), 0.01 g of aphotopolymerization initiator (Ilugacure 907, manufactured by Ciba-GeigyCo.) in 3.65 g of methyl ethyl ketone. The thickness of the liquidcrystal layer was adjusted so as to satisfy the condition of Rt′/Rt inTable 5 wherein Rt represents the retardation value in the thicknessdirection of the liquid crystal layer, and Rt′ is the retardation valuein the thickness direction of the transparent support. Each of resultantcoatings was fixed by adhering a metal flame and was heated for 3minutes in a high temperature device at 130° C. so that the discoticcompound was oriented. Subsequently, each sample in nitrogen gas wasirradiated with radiation having an illuminance of 100 mW/cm² at 130° C.for 10 seconds, employing a high pressure mercury lamp, and theresultant orientation was fixed employing crosslinking reaction. Theresultant sample was set aside and cooled to room temperature to form aliquid crystal layer comprising the discotic compound. Thus, opticallyanisotropic film samples were obtained for each of Cellulose Ester FilmSamples 101 through 112. No liquid crystal layer was applied toCellulose Ester Film Sample 113, which was only employed as the sampleof the transparent support.

The thickness of a support, as well as a film coated with a liquidcrystal layer described below, was measured employing a micrometer. Thethickness of the liquid crystal layer was calculated based ondifferences in the thickness with the liquid crystal layer and withoutthe liquid crystal layer.

<Preparation of Polarizing Plate>

Each of the resultant optically isotropic films was subjected to alkalitreatment employing a 2.5N aqueous sodium hydroxide solution at 40° C.for 60 seconds, and washed for 3 minutes. Thus an alkali treated filmwas obtained.

Subsequently, a 120 μm thick polyvinyl alcohol film was immersed in 100weight parts of an aqueous solution comprised of one weight part ofiodine and 4 weight parts of boric acid, and subsequently was stretched4 times. Thus a polarizing film was prepared. Said alkali treated samplefilm was adhered onto one side of the resultant polarizing filmemploying a 5 percent aqueous completely saponified type polyvinylalcohol solution as the adhesive and further an 80 μm thick celluloseacetate film was subjected to alkali treatment in the same manner andadhered. Thus a polarizing plate sample was prepared.

<Evaluation of Viewing Angle>

The polarizing plate of an LA-1529HM type TFT-TN liquid crystal panelmanufactured by NEC Corp. was peeled off, and the optical compensationfilm provided between said polarizing plate and the liquid crystal panelwas also peeled off. The polarizing plate comprising each of opticallyanisotropic films, to which the liquid crystal layer shown in Table 2was applied employing the aforementioned method, was provided so thatthe optically anisotropic film side is positioned between the polarizerand the liquid crystal panel and was then attached. The adhesion of thispolarizing plate was carried out on both of the black light side and theimage observing side with respect to the liquid crystal panel. For eachsample, a monitor was driven employing a personal computer, and acontrast ratio during white/black display was measured employing anEz-Contrast of ELDIM Co. Regarding upper and lower, and right and left,each angle of the liquid crystal panel having a contrast of at least 10from the radial direction was measured and designated as the viewingangle. Three-grade evaluation was carried out based on the criteriashown below.

Evaluation Upper Lower Left Right C below 30 below 35 below 45 below 45degrees degrees degrees degrees B 30 to 40 35 to 40 45 to 55 45 to 55degrees degrees degrees degrees A 41 to 50 41 to 50 56 to 65 56 to 65degrees degrees degrees degrees

Viewing Angle 2

The polarizing plate of a VL-1530 liquid crystal panel manufactured byFujitsu was peeled off. Employing the method described above, apolarizing plate comprising each optically isotropic film, into whichthe liquid crystal layer shown in Table 2 was applied, was provided sothat the optically anisotropic film side was positioned between thepolarizer and the liquid crystal panel, and was attached. The adhesionof the polarizing plate was carried out on both of the black light sideand the image observing side. Further, employing the aforementionedviewing angle measurement method, substantial evaluation of the viewingangles at upper and lower as well as right and left was carried out.

Evaluation Upper Lower Left Right C below 45 below 45 below 50 below 50degrees degrees degrees degrees B 45 to 55 45 to 55 50 to 60 50 to 60degrees degrees degrees degrees A 56 degrees 56 degrees 61 degrees 61degrees or more or more or more or more

<Number of Luminescent Spots>

A transparent support, which was employed for an optically anisotropicfilm, was placed between two polarizing plates arranged in the rightangle with each other. Subsequently, light was irradiated onto onesurface of the polarizing plate and the number of luminescent spots per250 mm² of the opposite surface was determined employing a microscope.Determination was carried out for five randomly selected areas, and theaverage value was designated as the number of luminescent spots due toforeign matter particles.

At that time, a transmitted light source and a magnifying factor of 30were employed as conditions using the microscope.

<Profitability>

Material ratio during the production of the optically anisotropic filmwas evaluated to be A, B, and C. Criteria were such that as the amountof liquid crystalline compounds decreases, profitability is improved.

TABLE 5 Residual Com- Support Solvent at position Thickness Peeling inRT Value Sample No. in μm percent in nm Rt′/Rt 101 (1) 80 19 86 0.74 102(2) 80 11 106  0.41 103 (3) 80 40 80 0.88 104 (4) 80 65 74 1.04 105 (5)80 65 72 1.08 106 (6) 80 76 33 3.5  107 (7) 80 110  57 1.63 108 (8) 8075 31 3.84 109 (1) 120  41 120  0.25 110 (2) 120  45 114  0.32 111 (6)120  70 36 3.17 112 (7) 190  71 95 0.58 113 (8) 80 75 31 0   Number ofLuminescent Spots Profit- Viewing Viewing 5 to 50 μm Sample abilityAngle 1 Angle 2 50 μm or more 101 A A A 43 0 present invention 102 A B A39 0 present invention 103 B A A 49 0 present invention 104 B A A 52 0present invention 105 B A A 89 0 present invention 106 C A B 305  5 com-parative 107 C B A 320  16  com- parative 108 C A B 362  2 com- parative109 A B A 71 0 present invention 110 A B A 62 0 present invention 111 CB B 478  7 com- parative 112 A B A 853  31 com- parative 113 A C C — —com- parative

As can clearly be seen from Table 5, the optically anisotropic films ofthe present invention exhibit excellent profitability associated withproduction as well as effects for enhancing the viewing angle. Further,liquid display is not adversely affected due to the minimized number ofluminescent spots.

Comparative TAC has higher refractive index in the thickness direction.As a result, as the Rt value increases, the film thickness increases.Due to that, the number of luminescent spots increases to adverselyaffect the liquid crystal display. When the retardation value in thethickness direction is increased by applying a liquid crystal layerwithout increasing the film thickness, profitability decreases due tothe fact that liquid crystalline compounds are more expensive thanresins which structure the support.

Example 5

Samples were prepared in the same manner as Example 1, except that LC-2instead of LC-1 was applied to the transparent support of Example 1employing the method described below, and subsequently were evaluated.

Ten weight percent of a solution was prepared by dissolving 5 g of LC-2in chloroform. This solution was applied employing a print method onto a30×30 cm square polyimide film which had be subjected to rubbingtreatment. Subsequently, the resultant coating was dried on a hot plateat 80° C. and was subjected to heat treatment at 230° C. for 20 minutesin an oven. Thereafter, the coating was removed from the oven and cooledto room temperature. First, LC-2 was oriented on the resultant polyimidefilm, and subsequently fixed. Next an ultraviolet hardening typeadhesive was applied onto the resultant liquid crystal layer. Thereafterlamination was carried out employing each of transparent supportsdescribed in Table 2, and the adhesive was hardened by radiation of ahigh pressure mercury lamp. Next, the resultant polyimide film waspeeled off and removed. The liquid crystal layer remained on thetransparent support via the adhesive. The adhesion layer was opticallyisotropic.

Resultant samples were evaluated in the same manner as Example 4. Theoptically anisotropic films of the present invention exhibited the sameeffects as Example 4, compared to comparative examples.

Example 5

Samples were prepared in the same manner as Example 4, except that LC-3instead of LC-1 was applied to the transparent support of Example 4,employing the method described below, and subsequently were evaluated.

Employing a wire bar, onto an alignment layer which was similar toExample 4, applied was a coating composition prepared by dissolving 1.6g of LC-3, 0.4 g of phenoxydiethylene glycol acrylate (M101,manufactured by Toa Gosei Co., Ltd.), 0.01 g of a photopolymerizationinitiator (Ilugacure 907, manufactured by Ciba-Geigy Co.) in 3.65 g ofmethyl ethyl ketone. The thickness of the liquid crystal layer wasadjusted so as to satisfy the condition of Rt′/Rt in the same manner asTable 2 of Example 1 wherein Rt represents the retardation value in thethickness direction of the liquid crystal layer, and Rt′ is theretardation value in the thickness direction of the transparent support.Each of resultant coatings was fixed by adhering a metal flame and washeated for 3 minutes in a high temperature device at 130° C. so that theliquid crystalline compound was oriented. Subsequently, each sample innitrogen gas was irradiated with radiation having an illuminance of 100mW (500 mJ)/cm² at 120° C. for 10 seconds, employing a high pressuremercury lamp, and the resultant orientation was fixed employingcrosslinking reaction. The resultant sample was set aside and cooled toroom temperature to form an optically anisotropic film comprising LC-3.

The resultant samples were evaluated in the same manner as Example 4.The optically anisotropic films of the present invention exhibited thesame effects as Example 4, compared to comparative examples.

It is possible to provide a film for a liquid crystal display which iscapable of improving optically anisotropic performance, such asminimizing problems due to abnormal light emission, enhancement of aviewing angle without increasing of the thickness, and the like, andprovide a polarizing plate as well as a liquid crystal display using thesame. In addition, it is possible to provide a film for a liquid crystaldisplay which is less expensive as well as thinner, while exhibitinghigher tear strength as well as excellent water resistance, and providea polarizing plate as well as a liquid crystal display using the same.

Disclosed embodiment can be varied by a skilled person without departingfrom the spirit and scope of the invention.

What is claimed is:
 1. An optically anisotropic film comprising: asupport which contains a fatty acid cellulose ester having an acyl groupincluding 2 or 3 carbon atoms, provided thereon an alignment layer and aliquid crystal layer, wherein the support has a relationship representedby Formula (1), a retardation value (Rt value) of the supportrepresented by Formula (II) is 50 to 300 nm, the number of luminescentpoints having a size exceeding 50 μm the support observed in crossNicole state is zero per 250 mm² and the number of luminescent pointshaving a size of 5 to 50 μm of the support observed in cross Nicolestate is 200 or less per 250 mm², Formula (I) (nx+ny)/2−nz>0 Formula(II) [(nx+ny)/2−nz]×d wherein nx represents the refractive index of thesupport in the direction giving maximum refractive index in the plane ofthe support, ny represents the refractive index of the support in thedirection perpendicular to the direction giving maximum refractive indexin the plane of the support, nz represents the refractive index of thesupport in the thickness direction and d represents the thickness (innm) of the support.
 2. The optically anisotropic film of claim 1 whereinthe retardation value (Rt value) represented by the Formula (II) is from60 to 250 nm.
 3. The optically anisotropic film of claim 1 wherein thethickness of the film is from 40 to 150 μm.
 4. The optically anisotropicfilm of claim 1 wherein the Rt ratio of the liquid crystal layer to thesupport represented by Formula 3 is 1.2 or less, Formula 3 Rt ratio(Rt′/Rt).
 5. The optically anisotropic film of claim 1 wherein the RTratio of the liquid crystal layer to the support represented by Formula4 is 1.2 or less, Formula (4) Rt ratio=(Rt′/Rt).
 6. The opticallyanisotropic film of claim 1 wherein the liquid crystal mode is twistnematic mode or a vertical alignment mode.
 7. The optically anisotropicfilm of claim 1 wherein the liquid crystalline compound constituting theliquid crystal layer is a monomer having a chemically reactive group andafter being oriented on the alignment layer, said orientation is fixedwhile being hardened by light or heat.
 8. The optically anisotropic filmof claim 1 wherein a liquid crystalline compound constituting the liquidcrystal layer is a discotic liquid crystal or a liquid crystallinepolymer.
 9. The optically anisotropic film of claim 1 wherein the numberof luminescent points having a size of 5 to 50 μm of the support incross Nicole state is 100 or less per 250 mm².
 10. An opticallyanisotropic film comprising: a support which contains a fatty acidcellulose ester having an acyl group including 2 or 3 carbon atoms,provided thereon an alignment layer and a liquid crystal layer, whereinthe support comprises fine particles having an average particle size ofnot more than 0.1 μm, the support has a relationship represented byFormula (I), a retardation value (Rt value) of the support representedby Formula (II) is 50 to 300 nm, the number of luminescent points havinga size exceeding 50 μm of the support observed in cross Nicole state iszero per 250 mm² and the number of luminescent points having a size of 5to 50 μm of the support observed in cross Nicole state is 200 or lessper 250 mm², Formula (I) (nx+ny)/2−nz>0 Formula (II) [(nx+ny)/2−nz]×dwherein nx represents the refractive index of the support in thedirection giving maximum refractive index in the plane of the support,ny represents the refractive index of the support in the directionperpendicular to the direction giving maximum refractive index in theplane of the support, nz represents the refractive index of the supportin the thickness direction and d represents the thickness (in nm) of thesupport.
 11. The optically anisotropic film of claim 10 wherein theretardation value (Rt value) represented by the Formula (II) is from 60to 250 nm.
 12. The optically anisotropic film of claim 1 wherein thethickness of the film is from 40 to 150 μm.
 13. The opticallyanisotropic film of claim 10 wherein the Rt ratio of the liquid crystallayer to the support represented by Formula 3 is 1.2 or less, Formula 3Rt ratio=(Rt′/Rt).
 14. The optically anisotropic film of claim 10wherein the Rt ratio of the liquid crystal layer to the supportrepresented by Formula 4 is 1.2 or less, Formula (4) Rt ratio=(Rt′/Rt).15. The optically anisotropic film of claim 10 wherein the liquidcrystal mode is twist nematic mode or a vertical alignment mode.
 16. Theoptically anisotropic film of claim 10 wherein the liquid crystallinecompound constituting the liquid crystal layer is a monomer having achemically reactive group and after being oriented on the alignmentlayer, said orientation is fixed while being hardened by light or heat.17. The optically anisotropic film of claim 10 wherein a liquidcrystalline compound constituting the liquid crystal layer is a discoticliquid crystal or a liquid crystalline polymer.
 18. The opticallyanisotropic film of claim 10 wherein the number of luminescent pointshaving a size of 5 to 50 μm of the support in cross Nicole state is 100or less per 250 mm².
 19. A vertical alignment (VA) type liquid crystaldisplay comprising a liquid crystal cell, a first optically anisotropicfilm provided on one said of the cell and a second optically anisotropicfilm provided on the other side of the cell, wherein each of the firstoptically anisotropic film and the second optically anisotropic filmcomprises, a support which contains a fatty acid cellulose ester havingan acyl group including 2 or 3 carbon atoms, provided thereon analignment layer and a liquid crystal layer, the support has arelationship represented by Formula (I), a retardation value (Rt value)of the support represented by Formula (II) is 50 to 300 nm, the numberof luminescent points having a size exceeding 50 μm of the supportobserved in cross Nicole state is zero per 250 mm² and the number ofluminescent points having a size of 5 to 50 μm of the support observedin cross Nicole state is 200 or less per 250 mm², Formula (I)(nx+ny)/2−nz>0 Formula (II) [(nx+ny)/2−nz]×d  wherein nx represents therefractive index of the support in the direction giving maximumrefractive index in the plane of the support, ny represents therefractive index of the support in the direction perpendicular to thedirection giving maximum refractive index in the plane of the support,nz represents the refractive index of the support in the thicknessdirection and d represents the thickness (in nm) of the support.
 20. Thevertical alignment (VA) type liquid crystal display of claim 19 whereinthe retardation value (Rt value) represented by the Formula (II) is from60 to 250 nm.
 21. The vertical alignment (VA) type liquid crystaldisplay of claim 19 wherein the thickness of each of the films is from40 to 150 μm.
 22. The vertical alignment (VA) type liquid crystaldisplay of claim 19 wherein the Rt ratio of the liquid crystal layer tothe support represented by Formula 3 is 1.2 or less, Formula 3 Rtratio=(Rt′/Rt).
 23. The vertical alignment (VA) type liquid crystaldisplay of claim 19 wherein the Rt ratio of the liquid crystal layer tothe support represented by Formula 4 is 1.2 or less, Formula (4) Rtratio=(Rt′/Rt).
 24. The vertical alignment (VA) type liquid crystaldisplay of claim 19 wherein the liquid crystalline compound constitutingthe liquid crystal layer is a monomer having a chemically reactive groupand after being oriented on the alignment layer, said orientation isfixed while being hardened by light or heat.
 25. The vertical alignment(VA) type liquid crystal display of claim 19 wherein a liquidcrystalline compound constituting the liquid crystal layer is a discoticliquid crystal or a liquid crystalline polymer.
 26. The verticalalignment (VA) type liquid crystal display of claim 19 wherein thenumber of luminescent points in each of the supports having a size of 5to 50 μm of the support in cross Nicole state is 100 or less per 250mm².
 27. The vertical alignment (VA) type liquid crystal display ofclaim 19 wherein each of the supports comprises fine particles having anaverage particle size of not more than 0.1 μm in an amount of 0.005 to0.3 weight parts per 100 weight parts of the support.